1. Field of the Invention
The present invention relates to an image-taking apparatus and image-taking method, suitably used with an electronic zoom image-taking system using a high-resolution image-taking apparatus.
2. Description of the Related Art
In recent years, electronic image-taking apparatus, such as electronic still cameras or the like, wherein a subject image is converted into electric signals by a photo-electric converter such as a CCD (charge-coupled device), subjected to predetermined digital signals processing, and then recorded in a recording medium such as a memory card or the like, are coming into widespread use. Some of the electronic image-taking apparatus have optical zoom functions, or electronic zoom functions wherein the subject image can be enlarged or reduced electronically, in order to deal with the multi-functionality in recent years.
Electronic zoom functions enable image signals for recording which can be recorded by an electronic camera, or image signals recorded in a recording medium, to be subjected to image processing wherein a part of the image is electrically enlarged, and the enlarged image is displayed on the entire screen area on a display screen of an image display unit.
Using this function allows an image wherein only a part of the image is enlarged to be obtained (photographed and/or recorded) or reproduced, aside from the image having a predetermined photography range stipulated by the photography optical system of the electronic camera.
Now, in recent years, the increase in the number of pixels of solid-state image sensors for still image taking has been marked. In the event of attempting to apply such solid-state image sensors for still image taking to moving images, a great amount of time is required for reading out all the pixels. Accordingly, subsampling scanning may be performed, taking into consideration a match with the image size of the display system.
Further, Japanese Unexamined Patent Application Publication No. 2000-295530 discloses a proposal for a method for performing electronic zooming by changing the subsampling ratio. FIGS. 1A and 1B are explanatory diagrams for describing the reading out according to this proposal. FIG. 1A illustrates reading out when in the normal mode, and FIG. 1B illustrates reading out when in the zoom mode.
In the normal mode, every other pixel of the solid-state image sensor is read out. For example, in the range within the heavy border shown in FIG. 1A, the signals of the pixels filled in are read out. That is to say, by performing reading out with a subsampling ratio of 2, wherein every other pixel is read out from an 8×8 vertical and horizontal range so as to read out signals for 4×4 pixels, the number of pixels read out can be reduced, thereby shortening the read-out time and the signal processing time.
Conversely, in the zoom mode, the continuous 4×4 pixels at the center of the range with the heavy border of 8×8 pixels (the filled in portion) are read out. That is to say, in this case, the center portion of the range with the heavy border (the portion filled in) can be enlarged and displayed, by performing reading out with a subsampling ratio of 1. Moreover, the number of pixels read out is the same as with the normal mode, so the read-out time and the signal processing time may be made to be the same as with the normal mode, thereby standardizing signal processing.
However, with the proposal in Japanese Unexamined Patent Application Publication No. 2000-295530, the subsampling ratio which is applicable in the zoom mode is determined according to the maximum subsampling ratio. For example, in the example in FIGS. 1A and 1B, the solid-state image sensor only has twice the number of pixels in both the vertical and horizontal directions of the number of pixels read when in the normal mode, so the maximum subsampling ratio is also 2. Accordingly, the subsampling ratio at the time of the zoom mode is fixed at 1. Further, there has also been the problem that only zoom operations wherein the zoom ratio is an integer (2, in the case of FIGS. 1A and 1B) are performed.
Also, the read-out range of the solid-state image sensor may be changed due to transition to the zoom mode, etc. In this case, in the event that the read-out area changes while performing read-out scanning, the read-out line from the scanning of the area before the change and the read-out line from the scanning of the area following the change are both simultaneously read out, which has been a problem in that suitable image-taking information cannot be obtained.